<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Title</title>
    <script src="./lib/vue.js"></script>
</head>
<body>
<!--Vue实例所控制的这个元素区域，就是我们的V-->
<div id="app">
    <input type="text" v-model="firstname"> +
    <input type="text" v-model="lastname"> =
    <input type="text" v-model="fullname">
</div>
<script>
    // 创建Vue实例，得到ViewModel
    var vm = new Vue({
        el: '#app',
        data: {
            firstname: '',
            lastname: '',
            fullname: '',
        },
        methods: {},
        watch: { // 使用这个 属性，可以监视 data 中指定数据的变化，然后触发这个 watch 中对应的 function 处理函数
            'firstname': function (newVal, oldVal) {
                // console.log('监视到了 firstname 的变化')
                // this.fullname = this.firstname + '-' + this.lastname
                this.fullname = newVal + '-' + this.lastname
            },
            'lastname': function (newVal) {
                this.fullname = this.firstname + '-' + newVal
            }
        }
    })
</script>
</body>
</html>